Geochemical constraints on blueschist- and amphibolite-facies rocks of the Central Cordillera of Colombia: the Andean Barragán region

Abstract

Subduction zones are one of the most characteristic features of planet Earth. Convergent plate junctions exert enormous influence on the formation and recycling of continental crust, and they are also responsible for major mineral resources and earthquakes, which are of crucial importance for society. A subduction-related geologic unit containing high-pressure rocks occurs in the Barragán area (Valle del Cauca Department) on the western flank of the Central Cordillera of the Colombian Andes. Blueschists and amphibolites, serpentinized meta-ultramafic rocks, graphite-chlorite-muscovite-quartz schists, protocataclasites, and graphite-chlorite-andalusite-andesine-garnet-muscovite ± titanite schists are exposed in this region. In spite of the petrotectonic importance of blueschists, the high-pressure metamorphism of the Central Cordillera of Colombia has been rarely studied. New geochemical data indicate that protoliths of the blueschist- and amphibolite-facies rocks possessed normal mid-ocean ridge basalt bulk compositions. 40Ar/39Ar geochronology for a metapelite rock associated with the blueschists shows a plateau age of ∼120 million years. We suggest that high-P/T conditions were present from ∼150 to 125 Ma, depending on the model of generation and exhumation considered.